A large amount of ultrapure water used as cleaning water in the production of electronic devices (in particular, semiconductor devices) is produced through treatment of raw water (e.g., industrial water, tap water, well water, or used ultrapure water discharged from electronic device plants) by an ultrapure water producing system including a pretreatment system, a primary water purification system, and a subsystem.
For example, PTL 1 discloses an apparatus for producing ultrapure water including a primary water purification system and a subsystem for treating the water from the primary water purification system, at least the primary water purification system including a reverse osmotic membrane separation unit, wherein the reverse osmotic membrane separation unit installed in the primary water purification system is a high-pressure reverse osmotic membrane separation unit installed in a single stage. PTL 2 discloses an apparatus for producing ultrapure water including a pretreatment system, a primary water purification system for treating the water treated by the pretreatment system to prepare primary pure water, and a subsystem for treating the primary pure water, wherein the primary water purification system includes a reverse osmotic membrane separation unit, a degassing unit, an electrodeionization unit, an ultraviolet oxidation unit, and a non-recycle ion-exchange unit in this order.
PTL 3 discloses an apparatus for producing ultrapure water including a primary water purification system and a secondary water purification system, wherein the primary water purification system includes a combination of a two-bed three-tower ion-exchange unit, a reverse osmotic membrane unit, an ultraviolet irradiation unit having a low-pressure ultraviolet lamp emitting ultraviolet rays of 180 to 190 nm, and a mixed-bed ion-exchange unit, the combination being disposed along a flow channel, and the secondary water purification system includes at least one combination of an ultraviolet irradiation unit having a low-pressure ultraviolet lamp emitting ultraviolet rays of 180 to 190 nm and a mixed-bed ion-exchange unit, the combination being disposed along a flow channel.
PTL 4 discloses an apparatus for producing ultrapure water including a pretreatment system, a primary water purification system, and a secondary water purification system, wherein each of the primary and secondary water purification systems includes at least one combination of an ultraviolet irradiation unit having a low-pressure ultraviolet lamp emitting ultraviolet rays of 180 to 190 nm and a mixed-bed ion-exchange unit, the combination being disposed along a flow channel.